Global warming may spawn wind shear able to hobble hurricanes, study finds

In the doomsday catastrophe of global warming - when Mar-a-Lago is submerged, Lake Okeechobee is an ocean bay and the Wellington polo fields are oceanfront property - rises a glimmer of good news.

Hurricanes spawned in the Atlantic Ocean may not be as monstrous or intense as some scientists have predicted.

Could global warming be a good thing for South Florida or whatever's left of it?

A pair of climatologists, one at the University of Miami and one in Princeton, N.J., think so.

"The environmental changes found here do not suggest a strong increase in tropical Atlantic hurricane activity during the 21st century," said coauthor Brian Soden, associate professor of meteorology and physical oceanography at the Rosenstiel School at the University of Miami.

Ever-warming seas - the very reason for more and bigger hurricanes - may foster milder winds in the Pacific Ocean, resulting in more wind shear in the Atlantic basin, stunting the growth of storms and slicing through those that do form.

"That's good for whatever part of Florida will still be above sea level," said Assistant Palm Beach County Administrator Vince Bonvento, who heads emergency management efforts.

Soden and lead author Gabriel Vecchi studied 100-year projections made by 18 global computer models to reach their findings, which will be published today in the American Geophysical Union's Geophysical Research Letters.

This is the first study to say that wind shear may counteract the increase in numbers and strength of hurricanes caused by global warming. "In fact, the wind shear changes are driven by global warming," Soden said.

"The collection of models consistently showed an increase in wind shear over the Atlantic and the eastern Pacific," he said.

On the other hand, the western Pacific and the Indian Ocean would receive the effect of warmer ocean water and less wind shear: the super storms.

The study concentrated on wind shear over the tropical Atlantic and its correlation with the Pacific Walker circulation, the immense loop of winds that affects climate across the globe. The slower the Walker circulation, the stronger the wind shear.

North of the equator, hurricanes are sheared when high-altitude westerly winds slice the tops of hurricanes pushed by low-altitude easterly winds.

Other scientists say that although Soden and Vecchi's conclusions based on the computer models are good, the models themselves aren't so good.

"Not a single model gets El NiÒo correct," said retired state climatologist Jim O'Brien, professor emeritus at Florida State University. "One has a permanent El NiÒo, and another has El NiÒo every other year."

El NiÒo, warmer-than-average Pacific equatorial water off the South American coast, helps slow the Walker circulation.

Nevertheless, O'Brien is one of the scientists who doesn't believe global warming is responsible for the current cycle of intense storms in the Atlantic. "The total number of storms worldwide is about the same, it just depends on the ocean," he said.

Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colo., doesn't trust the models either. "They don't have hurricanes, and they don't do El NiÒo correctly," he said. "With so little confidence, why should we believe this result?"

Even if the study's conclusions are correct on average, that doesn't mean there won't be years like 2005 with 28 named storms and seven major hurricanes.

"This certainly isn't the last word on global warming," Soden said. "There's a lot of debate about how clearly they're (connected). There will be a lot more research on this."

He also said it's not yet possible to tell how much the increased wind shear will offset the strength of storms strengthened by higher ocean temperatures.

"For those who are just being born, it's good news," said Palm Beach County's Bonvento. "For us middle-aged and older, be prepared."